Telephonic receiving apparatus



1,645,284 Oct. 11, 1927. R HINTON I TELEPHONIC RECEIVING APPARATUS Filed Sept. 27, 1924 2 Sheets-Sheet ,1

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WITNESSES: INVENTOR Patented Oct. 11, 1927.

UNITED STATES 1,645,284 PATENT OFFICE.

NORMAN PULLEN HINTON, F GOLDERS GREEN, ENGLAND, AS SIGNOR T0 METRO- IPOLITAN-VICKERS ELECTRICAL COMPANY, LIMITED, A BRITISH COMPANY.

TELEPHONIC RECEIVING APPARATUS.

Application filed september 27, 1924, Serial No.

This invention relates to telephonic receiving apparatus such for example as so-called note amplifiers for loud speakers and the like used'in the reception of wireless and other telephony.

' It is well known that telephonic receivers such as loud speakers have one or more prominent resonant points due to several causes such'as the natural resonance of the diaphragm and of the horn. Furthermore, an electrical amplifier using thermionic valves and transformers may also give prominence to currents of a particular frequency. Also speech and music may be distorted for various reasons at the transmitter due to resonance inherent in various parts of the transmitting apparatus and in the case of orchestral music to the unsuitable location of the different instruments with respect to the microphone or other sound receiving device.

The object of the present invention is to provide means for counteracting the effect of such resonance points, and thereby obtaining a smooth output corresponding to the original sound for all frequencies. The general tone and quality of the speech and music received on telephones and more especially on loud speakers can thusbe improved or varied.

According to the present invention means are provided for introducing other or similar resonant points into the amplification system at predetermined frequencies, and

for varying the sharpness of resonance at such points.

In carrying out the invention an electrical resonant circuit is associated with the input or output circuits of the amplifier or with 40 an intermediate circuit thereof the resonant frequency of said resonant circuit being capable of variation.

Preferably, the resonant circuit comprises an inductance and a variable capacity in parallel, the resistance of this circuit being preferably high. Thecircuit is connected across the terminals of the loud speaker or telephones, and may be reactively coupled to the input circuit of the note amplifier or to an intermediate circuit thereof, the extent of reaction being made variable to vary the effective resistance in the resonant circuit and consequently the sharpness of resonance therein. The variable resonance circuit provides a partial short circuit for 740,169, and in Great Britain October 16, 1923.

all audio frequency currents except those of the range of frequencies embracing the frequency to which the circuit is tuned whereby undesired frequency components of the speech or music may be excluded from the loud speaker or their prominence re duced.

In order that the invention can be fully understood it will now be described with reference to the accompanying drawings. Fig. 1 is an electrical diagram of a note amplifier and a loud speaker, provided with the improved tone adjusting means, and Fig. 2 is a modification of this arrangement. Fig. 3 is an electrical diagram of a low frequency amplification arrangement provided with internal tone adjusting means. Fig. 4 illustrates a further modification of the arrangements shown in Figs. 1 and 2. Fig. 5 is an electrical diagram of a plurality of note amplifiers associated with a single loud speaker, and Fig. 6 is a curve illustrating the operation of this arrangement.

Referring to Fig. 1 the anode and cathode of the detector valve 1 are respectively connected to the input terminals of the note amplifier 2, which preferably comprises any well known arrangementof three electrode valves and low frequency transformers. A loud speaker or telephone 3 is connected across the output terminals of the note amplifier, and an adjustable resonant circuit 4 is connected in parallel with the loud speaker. This resonant circuit comprises an inductance coil 5 in parallel with an adjustable condenser 6. A. high resistance 7 is preferably included in this resonant circuit. An inductance coil 8 is included in series in the input circuit of the note amplifier 2 and is adapted to react with the coil 5 of the resonant circuit 4.

A modification of the arrangement in Fig. 1 is shown in Fig. 2. The resonant circuit 4 comprising the inductance coil 5, the adjustable condenser 6 and the high resistance 7 is connected across the input terminals of the note amplifier 2, and the reaction coil 8 is connected in series with the loud speaker 3 in the output circuit of the amplifier.

In these two arrangements incoming signals are applied to the grid of the detector valve 1, the resultant detected signals being amplified in the note amplifier 2, and received in the loud speaker or telephone The note amplifier and the loud speaker both have characteristic resonance curves with maxima at definite frequencies. These maxima are preferably arranged to occur at different points in the frequency range suitable forthe loud speaker. The resonant, circuit at in either of the arrangementsin Fig. 1 or Fig. 2 offers a partial short circuit preferably of high resistance, to all low requency currents except those close to its own natural frequency. It is therefore tuned to a predetermined intermediate frequency between the maximum resonant frequencies of the note amplifier and the loud speaker respectively, so that currents of these frequencies are reduced in intensity and currents of intermediate frequencies passed unchanged. A smoother output for the. loud speaker corresponding to the original sound is thereby obtained. By the use of reaction between the resonant circuit and an intermediate circuit the effective resistance of the resonant circuit can be varied and hence the sharpness of resonance, which depends on the resistance, adjusted. A further control of the output tone can thus be effected.

Fig. 3 illustrates the application of the invention to a low frequency amplifier. In this arrangement the secondary of the low frequency transformer 10 is connected to the grid 11 of a three-electrode valve 12. The anode. of this valve is connected to the primary of the transformer 13 the seconda of which is connected to the grid 14 of the valve 15. The anode of this valve is similarly connected to the primary of the transformer 16 from the secondary terminals of which the amplified output can be delivered. The resonant circuit 4 is connected across the secondary of the transformer 13, that is to say, between the grid and cathode of the valve 15. The coil 8 is included in series with the primary of the transformer 16 in the anode circuit of the valve 15, and is adapted to react with the inductance coil 5 of the resonant circuit In this arrangement the resonant circuit 4 can be tuned to a frequencydifferent from the resonant frequency of the amplifier, and the sharpness of resonance adjusted by reaction to give a smooth resultant output. Or alternatively the amplifier resonant frequency or another frequency can be given prominence in the output which can then be applied to a loud speaker of telephone reso nant at a different frequency. 1

In Fig. l a modified form of the resonant circuit is shown applied to a note ,a1nplifie n and loud speaker. The anode and cathode of the detector valve 1 are respectively connected to the input termulals of the note amphlier across the output terminals of which the loud speaker 3 is connected. The modified resonant circuit 17 ,which is connected note amplifier and is adapted to react with I the inductance coil 18 of the resonant circuit 17 Alternatively the resonant circuit 1 can be connected across the input terminals of the amplifier and the reaction coil included in series with the loud speaker.

The modified resonant circuit 17 shown in Fig. 4 is adapted to act asa partial short circuit only to currents of frequencies close to its 'own natural frequency. To currents of other frequencies it acts as a choke. When connected in parallel with the loud speaker it is preferably tuned 'to the loud speaker resonant frequency so that currents of this frequency are reduced in intensity. The sharpness of resonance can be adjusted by means of the reaction coil 21, and the output tone thereby controlled.

amplifiers 22, 23, 24 their input terminals In Fig. 5 four note and 25 are shown with connected in series. The output terminals of the amplifiers are associated respectively with the low frequency transformers 26, 27, 28 and 29 whose secondaries are connected in series with a single loud speaker. The adjustable resonant circuits 30, 31, 32 and 33 are connected respectively across the primaries of the four transformers.

The action of this arrangement is illustrated by the curve shown in Fig. 6 in which the output energy of the amplifiers is plotted against the frequency of the note amplified. The maximum resonant points of the four amplifiers are shown respectively at the frequencies represented by 34, '35, 36 and 37. 38, 39, 40 and 41 are the corresponding resonance curves of the amplifiers. The approximate result-ant output of the four amplifiers is shown by the curve 42 ,which is obtained by addition of the ordinates of the four resmum resonance points of the amplifiers haye been shown' equally spaced through the range of frequencies employed and also each of the amplifiers has been shown with the same sharpness of resonance. This of course is not necessary or essential and the constants of the arrangement can be varied according to the conditions of use. For example if the loud speaker is strongly resonant or a certain band of frequencies the combined output from the amplifiers can be made correspondingly reduced for this band.

It is to be understood that various combinations of and modifications in the arrangements described can be made without departing from the scope of the invention.

Forexample the arrangements according to the invention may be incorporated with the loud speaker or with the note amplifier -onance curves. For convenience the maxior with an equipment comprising a combination of these devices, or the device may comprise a separate unit which may be used with any note amplifier and with any loud speaker or telephone receiver.

1 claim as my invention 1. In an audio-frequency amplifier, a plurality of amplifying units having their input circuits connected in series, a frequencyselective shunt connected across the out-put of each amplifier, the shunts being selective to different frequencies, transformers energized from the respective out-put of the amplifier and a circuit including a translating device connecting the secondaries of said transformers in series.

2. In an audio-frequency amplifier, a plurality of amplifying units having their input circuits connected in series, a frequencyselective shunt connected across the out-put of each amplifier, the shunts being selective to different frequencies, each shunt including a resistance, an adjustable feed-back coupling means for controlling the effective impedances of the several shunts,-transformers energized from the respective out-put of the amplifiers and a circuit including a translating device connecting the secondaries of said transformers in series.

In testimony whereof I have hereunto subscribed my name this l2th day of September, 1924.

NORMAN PULLEN HINTON. 

